Simple function to add submenu page to a custom post type menu in WordPress admin

add-submenu-page_to_custom_post_type_example.php

<?php 

// Hook 	

add_action('admin_menu', 'add_tutorial_cpt_submenu_example');

//Callback function 

function add_tutorial_cpt_submenu_example(){
	
	add_submenu_page(
						'edit.php?post_type=tutorial', //$parent_slug
						'Tutorial Subpage Example',  //$page_title
						'Tutorial Settings',        //$menu_title
						'manage_options',           //$capability
						'tutorial_subpage_example',//$menu_slug
						'tutorial_subpage_example_render_page'//$function
	);
}

//callback function 

function tutorial_subpage_example_render_page() { 

	echo '<h2> Tutorial Subpage Example </h2>'; 

}